Glycine and .alpha.- and .beta.-alanine are usually prepared by the reaction of ammonia with the respective hydroxy nitrile or acrylonitrile, to form the amino nitrile, then reacted with strong alkali to convert the cyanide moiety to the carboxylic acid salt of the alkali.
Typically, glycine, .alpha.-alanine and .beta.-alanine are recovered in their pure form by multiple extraction processes like that taught in U.S. Pat. No. 3,985,801. The patent teaches recovery of glycine from an aqueous solution of glycine and sodium chloride. The steps involved are: (1) adjusting the pH of the starting solution to 4.85-8.5 and evaporating water therefrom and cooling to precipitate glycine and to form a first mother liquor, (2) separating the precipitated glycine from the first mother liquor, and (3) recovering the separated glycine. In all, nine repetitive cycles are required to obtain 88.5% glycine reoovery. In a similar patent (U.S. Pat. No. 3,947,496) also issued to W. R. Grace and Company, sulfuric acid is substituted for hydrochloric acid. Eleven repetitive cycles are required to obtain 86% glycine and 84% Na.sub.2 SO.sub.4 recovery. U.S. Pat. No. 3,813,434, also issued to W. R. Grace and Company, teaches removal of iminodiacetic acid as an impurity in the glycine stream. Removal is accomplished by utilization of an anion exchange resin which retains the iminodiacetic acid component, thereby leaving a purified glycine solution.
These processes involve the production of salts and subsequently various waste streams.
Japanese Pat. No. 118,047 teaches utilization of either a three or four compartment cell similar to the one described in the present invention. Part of the technology taught in this patent is the addition of a portion of the anolyte (1N H.sub.2 SO.sub.4) to the middle stream (glycinate/glycine) in order to maintain conductivity in that stream. This addition results in the undesirable introduction of sulfate to the product stream, which eventually must be removed at additional cost. When the present invention is used, no conductivity enhancer is required to obtain 99.9% removal of sodium from the glycine stream. JP No. 118,047 further teaches that in order to reach conversions of sodium greater than 97.5%, either a four compartment cell or cation exchange bed is required. These two requirements are also unnecessary when the present invention is used. JP No. 118,047 cites an example in which sodium glycinate is converted to glycine by removal of 97.2% of the sodium charged. This is accomplished in a three compartment cell with the simultaneous production of 2N NaOH. The current density is 0.12 amp/cm.sup.2 (0.77 ASI) with an average cell voltage of 7.6 volts. No further data is given, therefore efficiency values may not be computed. However, it is known as current density is increased in an electrochemical process, the cell voltage rises proportionally. It is also known that as conversion approaches 100%, the voltage typically increases exponentially. Example 1 of the present invention produced 20.0 wt % NaOH at a current density of 2.09 amp/cm.sup.2 (1.5 ASI) with an average cell potential voltage of 5.68 volts.
It would be advantageous to process glycine, .alpha.- and/or .beta.-alanine to achieve a 99.sup.+ % recovery of the free acids at several times the rates of the prior art with voltage savings in the order of 1-2 volts. These advantages would result in increased capacity and less capital expenditure for the production of glycine from sodium glycinate.
The present invention utilizes a crude glycine stream and requires no extraneous additions of any kind. Not only is glycine produced, which is substantially free of glycinate, but also caustic which can be recycled to produce more glycinate.